The long term evolution (LTE for short) system has experienced several versions of R8/9/110, and R11 technique is researched successively and accurately. Currently, some R8 products start to be commercially used gradually, while R9 and R10 are waiting for further product planning.
After experiencing R8 and R9 periods, a number of new characteristics are further added to R10 on the basis of the former two, such as pilot frequency characteristics of DMRS (demodulation reference signal) and CSI-RS (channel state information reference signal), transmission and feedback characteristics of 8-antenna support, and especially, the eICIC (enhanced inter-cell interference cancelling) technique further considers the inter-cell interference avoiding technique on the basis of considering R8/9 ICIC. The technique for solving the inter-cell interference problem mainly considers cell interference avoiding in a homogeneous network in the early R10 period, and the eICIC technique and CoMP (coordinated multi-point) technique are main streams. As the name implies, CoMP is that multiple nodes coordinate with one node or multiple UEs send data over the same time frequency resource or different time frequency resources. Such a technique may reduce inter-cell interference, improve the throughput rate of cell edges, and enlarge the coverage of cells. However, in late discussion, since the heterogeneous network is taken into consideration and more scenarios are introduced, and due to the complexity of the CoMP technique and the time limit of R10 discussion, it is finally decided not to introduce additional CoMP standardized contents in the R10 period; however, when a CSI-RS is designed, it may be designed considering some requirements of the CoMP. Thus, the CoMP technique is not further discussed after the 60 bis conference.
In LTE a PDCCH (physical downlink control channel) bears scheduling allocation and other control information are defined. Each PDCCH is formed by several CCEs (control channel elements), and the number of CCEs of each subframe is determined by the number of PDCCHs and downlink bandwidth.
UE obtains the PDCCH by performing blind detection in a search space. The search space is divided into a common search space and a UE-specific search space. The common search space refers to a region where all the UEs may search, and this space carries cell-specific information. The specific search space refers to a space range where a single UE may search, and specific search spaces of multiple UEs may be overlapped, but generally only the initial search positions are different. Before the blind detection, higher layer signalling notifies the UE a work pattern and a radio network temporary identity (RNTI for short) type used for PDCCH cyclic redundancy check (CRC for short) scrambling.
Please see table 1 for the relationships among the search space Sk(L) and an aggregation level L and the number M(L) of candidate PDCCHs. The aggregation level is the number of CCEs occupied by the PDCCHs. When blind detection is performed in a UE-specific search space, a user equipment first calculates an initial blind detection position Yk according to UE identification (UE ID), a subframe number, etc., then performs detection in the search space, until a PDCCH allocated to the user equipment is detected.
TABLE 1PDCCH candidate setNumber ofSearch space Sk(L)candidateAggregationSize [number ofPDCCHsTypelevel LCCEs]M(L)UE specific16621264828162Common41648162
Please see table 2 for the corresponding relationship between the relative positions of the aggregation level and the first control channel element of the PDCCH in the UE-specific search space. The relative position of the first control channel element of the PDCCH in the UE-specific search space refers to the relative position of a first CCE index nCCE occupied by the PDCCH with respect to the initial blind detection position Yk, and nCCE, offset are used for representation in this text. nCCE, offset=nCCE-Yk, and the value range of nCCE, offset is 0-6, 8, 10. As shown in table 2, it is a schematic diagram of a possible first CCE position and an aggregation level corresponding thereto in the UE-specific search space.
TABLE 2Corresponding relationship betweenaggregation level and first CCE positionAggregationRelative position of the first CCE in thelevelUE-specific search spaceL = 1nCCE, offset = 0/1/2/3/4/5L = 2nCCE, offset = 0/2/4/6/8/10L = 3nCCE, offset = 0/4L = 4nCCE, offset = 0/8
In the latest 68 bis conference discussion process, feedback and interference definition assumptions are discussed in detail. Currently, the main view is to respectively conduct researches on channel measurement and interference measurement and channel measurement and interference are configured independently, and aggregation feedback of different CSI-RS resources may be supported, wherein the aggregation feedback comprises aggregation PMI feedback and aggregation CQI feedback. In addition, the overhead of feedback and that downlink control signaling and the size of a CoMP measurement set is relevant are considered; therefore, it is necessary to firstly discuss and limit the size of the CoMP measurement set, such that the feedback and downlink control signaling may acquire further discussion convergence. According to the 68 bis conference and offline discussion, it is primarily defined that the size of the CoMP measurement set is not greater than 2 or 3 at maximum, such that appropriate convergence may be performed on further feedback and control signaling researches.
With regard to the problem of how to configure the terminal side to feed back CSI required by the base station side in the related art, there is still no effective solution proposed currently.